Abstract
The present work to evaluate the effect of supplementation of urea release slow partial substitution of urea present in the common protein salt of heifers grazin Tifton-85 during the winter. The study was coducted in the period from May to September 2010. In an area of ??11.6 hectares of grazing Tifton-85 (Cynodon dactylon), divided into four paddocks of 2.9 acres, 36 heifers were kept testers (½ Red Angus ½ Nellore), treated as follows: Only mineralized salt (SM) protein salt with urea (SP); protein salt with 25% substitution of urea by slow degradation of urea (SPLD25) and protein salt with 50% substitution of urea by slow degradation of urea (SPLD50). There was no effect of different sources of supplementation on animal performance (P>0.05). However, differences were observed between the experimental periods, in consequence of the variation in chemical and structural composition of the forage.

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